In road construction, petroleum-derived asphalt and aggregate mixtures are applied to the road surface. These materials can be obtained by mixing anionic or cationic asphalt emulsions with aggregate, such as stone chips, gravel or sand, or by mixing free flowing heated asphalt with aggregate, by a hot mix or warm mix process. The quality of the road surface is generally dependent upon the strength of the bonds between the asphalt and aggregate. Rutting, or permanent deformation, is one of the main failure mechanisms for asphalt pavements. Excessive permanent deformation can occur in mixtures that lack adequate stiffness and/or strength at high temperatures. It is generally believed that tensile strength is a good indicator of mixture cohesion and can be related to the rutting potential of asphalt mixtures. Accordingly, it is desirable to develop asphalt binder modifiers that result in increased tensile strength and that reduce the potential for rutting.
Additionally, asphalt compositions can have relatively poor adhesion to aggregate in the presence of water. Generally, unless the aggregate is thoroughly dried, the aggregate surface remains wetted by water during blending with the asphalt, resulting in a weak boundary layer. Even if the surface of the aggregate is dry at the time it is blended with the asphalt, the eventual permeation of water from within an aggregate's micro- or meso-pores to the aggregate's surface, or the penetration of environmental water into the composition reaches the aggregate surface and interferes with the bond between the aggregate and the asphalt. This can result in stripping of the asphalt binder from the aggregate thereby weakening the adhesion between adjacent aggregate particles. In turn, under load of traffic this can lead to pavement failures including flaked pavement, “raveling”, cracking, and potholes.
To avoid such failures, adhesion-improving materials known as an anti-stripping agent (ASA) can be added to the asphalt. Before the mixing operation, ASAs are added to the petroleum-derived binder to reduce its surface tension and to induce on the binder an electrical charge opposite to that of the aggregate surface. Organic amines, have been traditionally used. They increase the hydrophobicity of the aggregate, making the aggregate resistant to the penetration of water so that water seeping towards the aggregate/asphalt interface does not tend to destroy the bond between the asphalt and the aggregate. Existing ASAs lack functional group diversity; e.g., liquid ASAs are generally derived from petroleum are alkyl or aryl amines or polyamines while solid ASAs are usually based on hydrated lime. Petroleum-derived amines used as ASA materials are primary alkyl amines such as lauryl amine and stearyl amine, and the alkylene diamines, such as the fatty alkyl substituted alkylene diamines. In addition to functional diversity, amine ASAs have concerns regarding heat stability at the high temperatures needed to adequately heat the binder. They can also be costly to synthesize.
Hydrated lime is a common anti-stripping agent and can be added by sprinkling it over the pre-wetted coarse aggregate or it may be added in the form of slurry. There are difficulties associated with both methods. There can be difficulty achieving adequate coating of the aggregate when adding hydrated lime in dry form. When added in a slurry form, there is an increase in cost associated with the fuel needed to heat the aggregate, and thus an increase in production cost. With both methods there are concerns related to health hazards due to inhalation and skin exposure. Accordingly, it is of interest to develop new anti-stripping agents that enhance the asphalt's adhesion to the aggregate in the presence of water and that avoid the issues associated with either amine ASAs or hydrated lime.
Recently, U.S. Patent Application 2010/0275817, entitled “Asphalt Materials Containing Bio-oil and Methods for Production Thereof,” has disclosed that bio-oil produced from the non-catalytic fast pyrolysis of a biomass can be used as an asphalt binder modifier. Non-catalytic fast pyrolysis produced bio-oils utilized by the 2010/0275817 application are characterized by being water soluble and having high oxygen content and high anhydro sugar content. Accordingly, because the composition of biomass derived oils vary greatly depending upon the processes used to derive the oil, bio-oil produced from non-catalytic fast pyrolysis is not indicative of whether other biomass derived oils may be used as an asphalt binder modifier.
Despite the environmental advantages of utilizing a renewable resource as the source for the asphalt binder modifier, it has been discovered that such non-catalytic fast pyrolysis bio-oils do not have a positive impact on tensile strength.
It would therefore be advantageous to have an asphalt binder modifier produced from a renewable source that results in improved tensile strength and enhanced adhesion of the asphalt to the aggregate in the presence of water. It would also be advantageous if such an asphalt binder modifier does not have a significant negative impact on the performance grade.